The purpose of the proposed project is to determine the hydrostatic pressure in the lymphatic and blood capillaries of rat intestinal villi under various conditions with possible changes of capillary permeability such as at elevated venous pressure during intra-arterial infusion of capillary permeability factors (histamine, bradykinin, etc.), during extracellular volume expansion of i.v. infusion of saline or during reinfusion of blood in hemorrhagic shock, and under the influence of cholera toxin with excessive secretion of fluid. The change of tissue fluid pressure under these conditions can be inferred from the change of the villus lymph pressure. The villus lymph and capillary pressures are determined by a micro-injection method of Landis with a newly developed in vivo rat intestinal preparation permitting micropuncture of the villus lymphatics and blood vessels for pressure measurement.